


Familiar Stranger

by CasualCazz



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell (Undertale), Cum Inflation, Knotting, M/M, Public Sex, Sanscest - Freeform, Size Difference, Underfell Sans (Undertale), kustard - Freeform
Language: English
Status: Completed
Published: 2018-12-13
Updated: 2018-12-13
Packaged: 2019-09-17 06:31:04
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 826
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16969467
Author URL: https://archiveofourown.org/users/CasualCazz/pseuds/CasualCazz
Summary: Red notices a copy of himself with a stupid face across the bar and decides to fuck with him.





	Familiar Stranger

**Author's Note:**

> This is a prize gift for the 100th person who followed me on Twitter! Sorry if this seemed a little rushed. I wanted to publish this before I went to work today. 
> 
>  
> 
> [My Twitter ](https://www.twitter.com/casualbones)
> 
>  
> 
> [Pillowfort ](https://www.pillowfort.io/casualbones)

Red glared at the skeleton across the bar from him, his scowl deepening as he watched a copy of himself chug a bottle of ketchup. Disgusting. How dare he wear Red’s face while drinking something so disgusting as tomato sauce. Mustard is clearly more superior. Though the copy wasn’t exact. The other skeleton’s teeth weren’t sharp and jagged like this, there was no crack running down his skull, however, he still had the same “I’m dead inside” quality about him, which Red could relate to. 

 

Still, seeing that face, really pissed him off. Taking another swig of alcoholic mustard drink, Red stumbled off his chair and made his way toward the other skeleton, then slammed his fist on the wooden table. Grillby only glared. 

 

“i gotta bone to pick with you,” Red hiccupped. 

 

The skeleton only raised his bone brow, “sorry buddy, i have a date with my trombone tonight,” 

 

“you think you can sit there, looking that. well, no sir. no siree. ain’t gonna happen, dollface,” he hiccuped and gripped the counter tightly. 

 

“yeah? and whatcha gonna do about it?” the skeleton challenged. 

 

Red squinted at the question, the cogs in his mind spinning too slowly to form a good coherent thought. His body, impatient with his slugness of his brain, acted on its own. He pulled the other skeleton by the shirt, and sloppily pressed their mouths together, in a clacking grind. 

 

“imma fuck you up,” Red snarled, his voice deep and low like gravel. 

 

The other skeleton’s eyes widened slightly and a faint blue blush spread across his cheeks, “k. name’s sans by the way.” 

 

“don’t care.” 

 

Grabbing Sans by the arm, Red teleported them both into a dark enclosed space, and shoved his copy against the nearest wall. His breath tingled on Sans’s neck, as he rubbed his hard shorts along the forming ecto-ass, pre-cum already soaking through the fabric. Sans squirmed, but Red restrained his wrists above his head.

 

“h-hey, wait, where are we?!” the smaller skeleton yelped. 

 

“grillby’s supply closet. didn’t want to lose energy by teleporting all the way home,” Red chuckled as he slapped pulled Sans’s pants down to his knees.

 

“what?! what if someone hears us-”

 

“then ya better not make a sound,” 

 

Yanking down his own pants, Red freed his growing erection, an average size dick, but with the girth of a fist and a knot double the size . He rubbed himself up and down Sans’s lose labias, coating himself in his juices for the bare minimum of lubrication. The small skeleton’s eyes bulge as he finally felt the size of his partner and opened his mouth to protest, but Red quickly covered it and leaned in for a whisper. 

 

“careful, we don’t wanna get caught,” 

 

Without any further warnings, Red shoved himself inside, completely knocking the wind out of his partner. Sans gasped and groaned at the sudden burn and fullness as his knees buckled, but Red wouldn’t let him fall. He thrusted away with feverish lust and without a single care in the world as the pussy clenched down on him tightly. Sans’s eyelights rolled to the back of his head as Red’s phalanges played with his tongue, drool dripping and splattering on his shirt. The thick knot pounded at his clit, sending vibrating shocks throughout his sensitive cunt.  

 

“so big…” he muttered dumbly as any thoughts poofed with a thrust. 

 

“fuck,” Red huffed, feeling himself close already, “yer gonna take my knott, ya hear me?” 

 

His rhythms increased with hot intensity, his head pounding hard at the cervix. 

 

“take it, you fucking b i t c h,” 

 

Red howled as he slammed his knot all the way inside, stretching Sans’s poor hole, and came like a geyser, his seed reaching the deepest depths of his partner. Sans bit down hard on his lover’s fingers, drawing blood, but Red didn’t care. As cum filled up his ecto womb, his stomach protrudded out slight to accommodate the mass and soon after, a rippling orgasm tore away at his core. Sans heaved and rested his head against the wall, and looked behind him. Red too, nearly at the point of passing out, but Sans just wanted to leave now.

 

“hey dude, you gotta get outta me,” he said nonchalantly. 

 

Through heavy breaths, Red looked down on himself, “uh, i can’t. we’re knotted.” 

 

Sans clenched his jaw and grabbed a sponge on the shelf, throwing it at this lover. 

 

“numbskull!” 

 

“hey! you saw my knot! you knew this was a possibility!” 

 

Before they could continue their argument, the door handle jiggled, and Grillby opened the closet door. Realizing too late that Sans was leaning on a door and not a wall,  he and Red came crashing to the ground in the middle of the restaurant, dick still inside pussy for the entire world to see. 

 

Grillby erupted into flames at the unsightly display, nearly turning the two skeletons into ash. 

 

Both of them are now banned forever. 


End file.
